1. Field of the Invention
The present invention relates to a radio packet data communication and, more particularly, to a system and method for controlling transmission of a radio packet data by using a transmission control protocol (TCP).
2. Description of the Background Art
In general, the TCP, a protocol widely used for a reliable data transmission, can be applied to various networks of the Internet. However, the performance of TCP is much degraded In a radio environment compared to a cable environment. The reason is because the bit error rate is high and a path is frequently changed due to a fading and a handoff, and if data loss is generated in the radio environment having a variable bandwidth, the TCP would determine that the data loss is caused by a network congestion and operate a congestion control mechanism.
This is because, in data protocol structure of a radio data service, as an upper TCP can not recognize whether a lower network section is a wireless section or a wired section, a radio link protocol (RLP), a lower network section, can not recognize which protocol is an upper layer.
Therefore, because the data protocol of the radio data service has such a structure that the RLP, the lower layer, can not transmit a transmission error of a radio section to the TCP, the upper layer, the TCP recognizes the transmission error as a network congestion and reduces the size of a transmission window to reduce data transmission. This causes degradation of performance between TCPs. Thus, without directly correcting the TCP so as not to operate the unnecessary congestion control mechanism, performance degradation of the TCP is inevitable.
FIG. 1 illustrates data protocol structure of a radio data service.
As shown in FIG. 1, the data protocol structure includes an RLP layer, a PPP (Point to Point Protocol) layer, an IP (Internet Protocol) layer, a TCP layer and an application layer.
When a user requests radio data service through a mobile station 101, a base station 102 performs a basic call setup process and an RLP setup process, and then opens a traffic path between a packet data serving node (PDSN) 103 and the mobile station 101. Then, the mobile station 101 is assigned an IP from the PDSN 103 through a PPP setup process of end PPPs, and is connected to an Ethernet network.
The RLP is a not-acknowledge (NAK)-based protocol devised for reducing an error rate generated during data transmission, including an RLP1 for IS-95A, an RLP2 for IS-95B, and an RLP3 for IS-2000.
In addition, in order to perform a PPP setup process between end PPPS, a relay layer is set up between the base station 102 and the PDSN 103, and the relay layer is described according to an IS-95 series standards for interfacing of air area.
That is, as shown in FIG. 2, when the packet data service is requested by the mobile station 101, data receiving block 110 of the base station 102 receives data from the PDSN 104 and transmits it to a RLP processing block 120. Then, the RLP processing block 120 processes the new data received from the data receiving block 110 according to the RLP protocol and transmits it to the mobile station 130. At this time, the new data is stored in a re-transmission buffer 21 and a temporary buffer 20.
During the packet data transmission, when re-transmission of data is requested by the mobile station 130, the RLP processing block 120 re-transmits the data frame stored in the temporary buffer 20.
The conventional radio packet data transmission method using the transmission control protocol will now be described with reference to FIG. 3
As shown in FIG. 3, the data receiving block 110 receives data from the PDSN (step S101) and transmits it to the RLP processing block 120.
Then, the RLP processing block 120 stores the received data in the re-transmission buffer 21 (step S103), performs an RLP processing on it, and transmits the processed RLP data to the mobile station 130 by using the RLP protocol
At this time, the RLP processing block 120 checks whether an NAK (Not Acknowledge) signal has been received from the mobile station 130 over the RLP data (step S109), that is, whether data re-transmission has been requested.
If there is no data re-transmission request, the data receiving block 110 continuously receives data from the PDSN (step S101). If, however, there is data re-transmission request, the data receiving block 110 re-transmits RLP data corresponding to a corresponding sequence from the re-transmission buffer 21 (step S111).
When the radio packet data service is used, the upper protocol is determined depending on a service that the mobile station 130 is provided with. In this respect, however, the RLP layer can not know information about the protocol of the upper layer, it transmits data with the same priority for every protocol.
That is, when a user receives data service using the TCP, the application layer capsulizes the user data by the TCP/IP. The capsulized data undergoes a PPP processing, divided according to an air section, undergoes an RLP processing, and is then transmitted to the mobile station 130 through a radio interface section.
While the RLP layer is transmitting sequential data according to the NAK based protocol, if a lost sequence is generated, the RLP layer transmits an NAK control frame to the sending side (base station), so as to receive data for the corresponding sequence from the base station. In preparation for a case that a re-transmitted frame is lost again, a rounding number is set so the base station performs re-transmission several times.
If, however, re-transmitted data is continuously lost, the mobile station aborts an RLP frame of a corresponding sequence, and sends an RLP frame of the next sequence to the upper layer (PPP→IP→TCP). If data does not have the RLP frame because of its loss, the PPP layer determines it as an error through a cyclic redundancy check (CRC), so the full frame is not transmitted to the TCP/IP layer.
Therefore, failing to receive the full frame, the TCP determines that the network is congested and operates a congestion control alrogithm, resulting in that the size of a transmission window is reduced and thus data transmission is reduced.
In other words, some transmission errors between the RLP ends causes a congestion control between the entire TCPs. However, the transmission error between the RLP ends occurs frequently in the radio section, so the TCP's congestion control may occur in great numbers in areas with a bad radio environment.
The problem is that the TCP, the upper layer, is made suitable for a cable environment which has little transmission error, whereas the RLP, the lower layer, does not have any information about the upper layer and is made suitable for a radio environment. Thus, with the current protocol structure where there is no communication between the TCP and the RLP, there is no way for the RLP to inform the TCP about the transmission error.
Accordingly, because the TCP can not discriminate case that the transmission error occurs and a case that the network congestion occurs, the transmission error at the RLP terminal can be mistakenly recognized as the network congestion. This would cause to operate of the unnecessary congestion control mechanism of the TCP. Then, the transfer rate is degraded and a reliable data service to users can be hardly expected.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background